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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

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GLACIERS NEAR THE COPPER RIVER DELTA                  891
expansion of Sheridan Glacier, rather than a westward expansion of the former Copper River Glacier.
A considerable portion of the main outwash gravel plain, north of the railway, and of the alluvial fan to the east of it, is forested; but where the present streams flow there are barren areas and extensive groves of dead trees, the lower portions of their trunks being deeply buried in gravel. The killing of mature spruces by alluviation was still in progress in 1910. South of the railway much of the outwash gravel plain is covered with swamp grass because it is too wet for tree growth, while still nearer the Pacific there are broad areas of salt marsh and mud flat.
Sherman Glacier—General Description. Sherman Glacier,1 occupying the valley east of Sheridan Glacier (PI. XCIII), has its main source 8200 feet above sea level in the mountains immediately west of the Copper River. It flows southwestward with a length of over 7| miles, and a width of 1$ miles, terminating entirely within its mountain valley.
Relation to Sheridan Glacier. Sheridan Glacier bulb completely overlaps the mouth of this valley, but Sherman Glacier supplies none of the ice of the present bulb. The early maps all show Sheridan and Sherman Glaciers uniting and forming a piedmont ice mass; but this was discovered to be an error by the junior author in 1910 and is correctly represented on Witherspoon's revised map of 1911. A view from the fan of outwash gravels makes it clear that Sherman Glacier is not a tributary, but an independent glacier, though the two may be in actual contact in a short portion of the area not visible from our point of observation. A rock hill rises through the Sheridan ice in one portion of the margin. The two glaciers may have fed one piedmont area at a more expanded stage of glaciation, but it is thought possible that botib ice tongues had receded into their mountain valleys before the Sheridan readvanced and formed the present ice bulb.
Tributaries. In addition to the ice supply from the 3200 foot divide, Sherman Glacier is fed by three or more steeply cascading tributaries, descending the slopes of Mt. Murchi-son2 from the north. Near the terminus there are two prominent hanging valleys out of the mouths of which cascading glaciers extend, though they do not now reach down to the surface of the main glacier. There are several weak medial moraines, but the surface of the glacier is very clean and little crevassed. Sherman Glacier though wider than Sheridan Glacier in its mountain valley, and with more medial moraines, and presumably more tributaries, is apparently at present the weaker of the two; for, as indicated above, it seems not to have participated in the advance which carried the bulb of the Sheridan out past the Sherman terminus.
Through Glacier. Rising on a broad snow divide, from which a smaller ice tongue extends eastward to the Copper River valley, Sherman Glacier is an excellent illustration of the type of through glacier, for which Hobbs8 has proposed another name, which to us seems much less suggestive, figuring this glacier as an example. The map upon which he based his figure 4 is an older one upon which the topographer transferred the name of Sheridan Glacier to Snennan Glacier, though Abercrombie, who named the former, applied it to the westernmost of these two ice tongues.
i Named in 1910 for General W. T. Sherman.
» Named in 1910 for S. Murchison, one of the engineers who was prominent in the building of the Copper River and Northwestern Railway.
• Hobbs, W. H., Characteristics of Existing Glaciers, New York, 1911, pp. 44-5. < Op. cit., Fig. 16, p. 45.